Technical Field
The description relates to semiconductor devices.
One or more embodiments may apply, e.g., to mounting Flip Chip dice on a substrate (e.g., with a high I/Os number) by using electrical contact pillars.
Description of the Related Art
Various methods may be adopted for connecting dice to substrates such as printed circuit boards—PCBs by using pillars. An electrolytic growth of metal (e.g., copper) on top of die pads, possibly with a topping of reflowable material (e.g., tin) at the top may be exemplary of such a pillar.
These methods may include e.g., mass reflow or thermo-compression.
Mass reflow is an operation performed in a controlled environment (e.g., in a temperature-controlled oven) to produce reflow of the topping material of the pillars on metal areas of a PCB in order to ensure electrical continuity.
Thermo-compression is an operation performed in order to provide for a certain time electrical contact of the pillars while the material between the die and a substrate undergoes curing to provide a force via shrinkage.
High temperature operation, which may induce stresses on joints, may be a critical factor in mass reflow.
A long cycle time may be a disadvantage of thermo-compression.
Both processes (mass reflow and a thermo-compression) may turn out to be critical in terms of package reliability, e.g., leading to a short life-on-board of components due to loss of electrical contact.
Also, deformation/damage of the topping material (e.g., tin) during pillar testing (EWS) may lead to the formation of “indents” where air may be trapped with the risk of causing failure of the electrical connection due to thermal stresses during application life.
Additionally, pillars located at the die corners may be subject to relevant shear and traction stresses due to different expansion coefficients of the semiconductor die (e.g., silicon) and the PCB (e.g., an organic substrate). Shear and traction stresses in those areas may lead to failure of the electrical connections.
Also, it was observed that ball grid array—BGA devices using, e.g., Cu pillars may not provide the same reliability levels of plastic packages, which may be a limiting factor in various areas such as the automotive sector.